Neurons have a quasi-amoeboid shape, consisting of a single long projection called an axon and shorter, typically branching projections called dendrites. Some types of neurons, such as Purkinje cells[?], have over 1000 dendrites. The body of a neuron, from which the axon and dendrites project, is called the soma and holds the nucleus of the cell. The nucleus typically occupies most of the volume of the soma and is much larger in diameter than the axon and dendrites, which typically are only about a micrometer thick or less. Neurons join to one another and to other cells through synapses.

A defining feature of neurons is their ability to become "electrically excited"--that is, to undergo an action potential--and to convey this excitation rapidly along their axons as an impulse. The narrow cross section of axons and dendrites lessens the metabolic expense of conducting action potentials, although fatter axons convey the impulses more rapidly, generally speaking.

Many neurons have insulating sheaths of myelin around their axons, which enable their action potentials to travel faster than in unmyelinated axons of the same diameter (see saltatory conduction under action potential). Formed by glial cells, the myelin sheathing normally runs along the axon in sections about 1 mm long, punctuated by unsheathed nodes of Ranvier[?]. Neurons and glia make up the two chief cell types of the nervous system.

An action potential that arrives at its terminus in one neuron may provoke an action potential in another through release of neurotransmitter molecules across the synaptic gap.